1. Technical Field
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device in which a copper-containing metal is employed as a material of an interconnect.
2. Related Art
Recently, copper has come to be popularly employed as a material for an interconnect, in response to the demand for higher integration level and faster operation speed of semiconductor devices. Copper has, in comparison with aluminum which has conventionally been employed, the advantage of lower resistance, as well as higher electromigration resistance.
The interconnect structure including copper is formed through what is known as a Damascene process, as described in Japanese Patent Laid-Open No. 2002-110679, including performing a chemical mechanical polishing (hereinafter, CMP) process after forming a copper layer. In the Damascene process, the CMP process is generally followed by a cleaning process.
Japanese Patent Laid-Open No. 2002-110679 points out that the cleaning process after the CMP incurs an increase in resistance of the interconnect. The literature also proposes, as a remedy therefor, that the semiconductor substrate that has undergone the CMP process be subjected to an alkali cleaning and an acid cleaning sequentially, and that the semiconductor substrate be subjected to a reduction process, either after the CMP and before the post-CMP cleaning or after the alkali cleaning and before the acid cleaning.
Among those cleaning processes, the acid cleaning is intended to improve time-dependent dielectric breakdown (hereinafter, TDDB) characteristic and remove a residual metal. Also, the literature states that the reduction process reduces the copper surface which has been once oxidized through the CMP process, to thereby enhance the resistance of the entire copper interconnect against the cleaning solution. This allows, according to the literature, suppressing formation of a step and etching corrosion on an upper portion of the copper interconnect, thereby suppressing the increase or fluctuation in resistance of the buried interconnect, which is predominantly composed of copper.
In addition, although in a different technical field, “Volatile Corrosion Inhibitor (VCI)”, Three-Bond Technical News, 18, p. 4, July 1, S62 states that benzotriazole (hereinafter, BTA), known as an anti-corrosion agent for copper, may form a different polymer compound depending on the ionic status of the copper.
Upon reviewing the Damascene process from the foregoing viewpoint, however, the present inventors have discovered that the method according to the Japanese Patent Laid-Open No. 2002-110679 still have a room for improvement with respect to suppressing degradation in TDDB resistance, because the interconnect has come to be formed in narrower spacing these days. The imperfect suppressing effect of the TDDB resistance degradation was prominently observed through the BTA processing performed after the acid cleaning in the post-CMP cleaning process. The degradation in TDDB resistance leads to loss of reliability in the semiconductor device, and hence has to be suppressed.